The present application relates to a cathode active material containing a lithium cobalt compound oxide containing lithium Li and cobalt Co and to a battery using the cathode active material.
In recent years, many portable electronic apparatuses have been developed and a secondary battery is occupying an important position as a power source of such an apparatus. Particularly, in recent years, the realization of a high capacitance and a light weight of the secondary battery is demanded. As a secondary battery which meets such a request, a lithium secondary battery using lithium as an electrode reactive substance has been put into practical use.
Lithium cobalt acid LiCoO2 is widely used as a cathode active material of the lithium secondary battery. This is because lithium cobalt acid has a stratified structure which is advantageous to diffuse lithium ions, the structure is stable even for doping and dedoping of the lithium ions, and excellent characteristics can be obtained. However, in recent years, use in a wider temperature range and use at a large current are also requested, and a request for the characteristics becomes further severe.
Therefore, many trials for improving the characteristics by replacing cobalt in lithium cobalt acid by another element or by adding another element have been made. For example, in Patent Document 1 (JP-A-2001-319652), there has been disclosed a cathode active material whose stability at a high temperature can be improved by replacing a part of cobalt by a first element of at least one kind selected from a group containing aluminum Al, chromium Cr, vanadium V, manganese Mn, and iron Fe and a second element of at least one kind selected from a group containing magnesium Mg and calcium Ca. In Patent Document 2 (JP-A-2004-311408), there has been disclosed a cathode active material in which when lithium cobalt acid is synthesized, a zirconium compound is coprecipitated and zirconium Zr is allowed to exist on a particle surface of lithium cobalt acid, so that load characteristics, low-temperature characteristics, and thermal stability can be improved.
However, according to the cathode active material disclosed in Patent Document 1, although the high-temperature characteristics can be improved, it is difficult to obtain the satisfactory characteristics with respect to the load characteristics and the low-temperature characteristics. It is also requested to further improve the cycle characteristics. According to the cathode active material disclosed in Patent Document 2, although the thermal stability can be improved, it is difficult to obtain the characteristics near the characteristics which have been requested in recent years.